linux-kernel - Re: [PATCH 00/19] tracing/workqueue: events support/enhancements, worklets tracing, fixes

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Date:	Thu, 30 Apr 2009 14:48:12 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Li Zefan <lizf@...fujitsu.com>,
	Zhao Lei <zhaolei@...fujitsu.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Tom Zanussi <tzanussi@...il.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Subject: Re: [PATCH 00/19] tracing/workqueue: events support/enhancements,
	worklets tracing, fixes

On Thu, Apr 30, 2009 at 10:45:29AM +0200, Ingo Molnar wrote:
> 
> * Frederic Weisbecker <fweisbec@...il.com> wrote:
> 
> > Hi,
> > 
> > This patchset brings various features for the workqueue tracer.
> > 
> > The support of events tracing (tracepoint expanding):
> > 	- workqueue_creation
> > 	- workqueue_flush
> > 	- workqueue_destruction
> > 
> >     Also for the worklets:
> > 	- worklet_enqueue
> > 	- worklet_enqueue_delayed
> > 	- worklet_execute
> > 	- worklet_complete
> > 	- worklet_cancel
> > 
> > Now, most of the lifecycle of worklets and workqueues is available.
> > 
> > The histogram tracing now also supports the worklets. You can
> > measure the max and average execution time of a worklet.
> > 
> > A good bunch of Oleg's comments have been addressed, at least the
> > critical ones (races which can cause freed pointer dereferences, memory
> > leak, etc...). The rest is more about the design itself, such as using
> > the workqueue as the identifier instead of the thread and other things
> > that are in discussion.
> > 
> > Thanks!
> > 
> > Frederic.
> > 
> > The following changes since commit a0e39ed378fb6ba916522764cd508fa7d42ad495:
> >   Heiko Carstens (1):
> >         tracing: fix build failure on s390
> > 
> > are available in the git repository at:
> > 
> >   git://git.kernel.org/pub/scm/linux/kernel/git/frederic/random-tracing.git tracing/workqueue
> > 
> > Frederic Weisbecker (6):
> >       tracing/workqueue: turn cpu_workqueue_stats::inserted into unsigned int
> >       tracing/workqueue: add execution time average column
> >       tracing/workqueue: add open/release file handlers
> >       tracing/workqueue: defer workqueue stat release if needed
> >       tracing/workqueue: use the original cpu affinity on probe_workqueue_destruction
> >       tracing/workqueue: provide documentation for the workqueue tracer
> > 
> > KOSAKI Motohiro (2):
> >       workqueue_tracepoint: introduce workqueue_handler_exit tracepoint and rename workqueue_execution to workqueue_handler_entry
> >       tracing/workqueue: add max execution time mesurement for per worklet
> > 
> > Zhaolei (11):
> >       ftrace, workqueuetrace: make workqueue tracepoints use TRACE_EVENT macro
> >       trace_workqueue: use list_for_each_entry() instead of list_for_each_entry_safe()
> >       trace_workqueue: remove cpu_workqueue_stats->first_entry
> >       trace_workqueue: remove blank line between each cpu
> >       trace_workqueue: add worklet information
> >       workqueue_tracepoint: add workqueue_flush and worklet_cancel tracepoint
> >       workqueue_tracepoint: change tracepoint name to fit worklet and workqueue lifecycle
> >       workqueue_trace: separate worklet_insertion into worklet_enqueue and worklet_enqueue_delayed
> >       tracing/workqueue: turn workfunc_stats::inserted into unsigned int
> >       tracing/workqueue: avoid accessing task_struct's member variable in stat file read
> >       tracing/workqueue: use list_for_each_entry instead of list_for_each_entry_safe in probe_workqueue_destruction()
> > 
> >  Documentation/trace/workqueue.txt |  114 ++++++++++
> >  include/trace/events/workqueue.h  |  200 +++++++++++++++++
> >  include/trace/workqueue.h         |   25 --
> >  kernel/trace/trace_stat.c         |    8 +
> >  kernel/trace/trace_stat.h         |    3 +
> >  kernel/trace/trace_workqueue.c    |  444 +++++++++++++++++++++++++++++--------
> >  kernel/workqueue.c                |   45 +++--
> >  7 files changed, 697 insertions(+), 142 deletions(-)
> >  create mode 100644 Documentation/trace/workqueue.txt
> >  create mode 100644 include/trace/events/workqueue.h
> >  delete mode 100644 include/trace/workqueue.h
> 
> I think one worry here - and this mirrors some of Andrew's concerns 
> - is the debug code to instrumented code ratio. There's 500 lines of 
> instrumentation for 1000 lines of code.
> 
> Is there a chance we can reduce that ratio, by factoring out bits of 
> kernel/trace/trace_workqueue.c and perhaps compressing 
> include/trace/events/workqueue.h some more?



Hehe, indeed. By adding code here and there, I guess we
forgot to unify common bits. I will try to factorize that.


 
> Also, it would be nice to check how intuitive it is to visualize 
> workqueue related details using the user-space ftrace-analyzer tool. 
> 
> Kernel developers are one thing - but most of the Linux developers 
> are user-space developers so any workqueue tracing details have to 
> be intuitive (and useful) to them. (even though workqueues are a 
> fundamentally in-kernel abstraction)
> 
> 	Ingo


Ok, I will see what it gives and give some examples.

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